1. Field of the Invention
The present invention relates to a single-pipe cylinder type reformer for manufacturing a hydrogen-rich reformed gas by steam-reforming a hydrocarbon-based crude fuel such as town gas, natural gas, or LPG or an alcohol and, more particularly, to a reformer used in combination with a polymer electrolyte fuel cell.
2. Description of the Prior Art
A reformer is an apparatus for producing a (hydrogen-rich) reformed gas having a high hydrogen concentration by steam-reforming a hydrocarbon-based crude fuel such as town gas, natural gas, and/or LPG or an alcohol. This apparatus is widely used to produce hydrogen used in the process of manufacturing optical fibers or semiconductors and for fuel cells and the like.
In a case of methane, the reforming reaction in the reformer is expressed as:
CH4+H2Oxe2x86x92CO+3H2(CH4+H2O←CO+3H2)
CO+H2Oxe2x86x92CO2+H2(CO+H2O←CO2+H2)
The steam reforming reaction caused by the reformer is an endothermic reaction, and hence heating is required to sustain the reaction. In general, a combustion unit such as a burner is provided for the reformer, and heating is performed by burning surplus hydrogen from a reformation material gas or fuel cell. As a reformer for producing a relatively small amount of hydrogen, a single-pipe cylinder type reformer like the one disclosed in Japanese Unexamined Patent Publication No. No. 11-11901 is known. This single-pipe cylinder type reformer is configured to have a heating means such as a burner in a cylindrical vessel incorporating a catalyst layer between two cylinders so as to heat the catalyst layer with the heating means and steam-reform a reformation material gas passed through the catalyst layer.
FIG. 1 is a longitudinal sectional view showing the schematic arrangement of a conventional single-pipe cylinder type reformer.
In the single-pipe cylinder type reformer shown in FIG. 1, an upright elongated outer cylinder 1 having a circular cross-section, a circular inner cylinder 3 located inside the outer cylinder 1, an intermediate cylinder 2 located inside the outer cylinder 1 to surround the inner cylinder 3 at a predetermined distance therefrom, and a radiation cylinder 4 located inside the inner cylinder 3 are concentrically disposed, and the annular space between the inner cylinder 3 and the intermediate cylinder 2 is filled with a reforming catalyst 5. A burner 7 supported on a burner mount base 6 is disposed in the upper portion of a combustion chamber 9 located inside the radiation cylinder 4. A cover plate (bottom plate) la which is a common one-piece plate is attached to the lower ends of the outer cylinder 1 and inner cylinder 3. In the single-pipe cylinder type reformer shown in FIG. 1, the burner 7 is disposed in the upper portion of the combustion chamber 9. However, the burner 7 is disposed in the lower portion of the combustion chamber 9 in some case (not shown). In such a case, the cover plate 1a is attached as a ceiling plate, which is a common one-piece disk, attached to the upper ends of the outer cylinder 1 and inner cylinder 3.
The single-pipe cylinder type reformer shown in FIG. 1 operates as follows.
The burner 7 generates a high-temperature combustion gas in the combustion chamber 9 with a combustion flame 8. The heat is transferred outside the inner cylinder in the radial direction via the radiation cylinder 4 to heat the reforming catalyst 5. At the same time, the high-temperature combustion gas enters the inner cylinder 3 from the lower portion of the radiation cylinder 4 to become an ascending current, thereby directly heating the reforming catalyst 5. The combustion gas is discharged from the upper end portion of the reformer after heating. Meanwhile, the reformation material gas which is fed from the upper portion of the reformer is heated to about 700xc2x0 C. while descending the annular flow path filled with the reforming catalyst 5. As a consequence, steam reforming is sufficiently performed. The reformed material gas (reformed gas) is reversed in the lower end portion of the reformer to become an ascending current in the path formed between the outer cylinder 1 and the inner cylinder 3. Meanwhile, the sensible heat of the reformed gas is recovered in the reforming step inside the intermediate cylinder 2. As a result, the temperature of the reformed gas lowers, and the gas is extracted outside as a reformed gas from the upper end portion of the reformer.
The conventional single-pipe cylinder type reformer shown in FIG. 1 suffers the following problems.
(1) Since the common one-piece cover plate 1a is hermetically fixed to the lower end portions of the outer cylinder 1 and inner cylinder 3, which require a partition for a fluid, by welding or the like, the thermal stresses produced in the outer cylinder 1 and inner cylinder 3 due to the temperature difference during operation cause buckling of the inner cylinder 3 which is heated to a high temperature, in particular. The following factors due to this buckling may degrade the performance of the reformer:
a. leakage of the reformed gas due to a crack in the inner cylinder 3;
b. damage to the reforming catalyst due to the deformation of the inner cylinder 3; and
c. uneven heating in the circumferential direction due to the deformation of the inner cylinder 3.
(2) Since the combustion chamber 9 is partitioned off from the outside with the one-piece cover plate 1a common to the inner cylinder 3 and outer cylinder 1, the heat insulating properties are poor, and the heat radiation loss from the cover plate 1a portion increases.
When a polymer electrolyte fuel cell is used for a home, vehicle, or the like, a reduction in the size and weight of the overall reforming apparatus including a single-pipe cylinder type reformer is an essential condition. In addition, various improvements, e.g., efficient operation and a reduction in rise time for the start of operation, are required.
For example, the required improvements include a reduction in fuel by efficient preheating of a reformation material gas, an improvement in operability by prevention of overheating of a steam generator, an increase in efficiency by the preservation of a necessary temperature inside the reformer and the effective use of heat quantity, suppression of heat radiation to the outside by an effective heat insulating structure, realization of high durability by a reduction in heat stress due to an inner temperature difference, an increase in efficiency of steam generation by the effective use of reaction heat, and an operation method capable of efficiently coping with variations in operation state.
The reformed gas produced by the conventional single-pipe cylinder type reformer contains about 10% of CO. When such a reformed gas is to be used for a polymer electrolyte fuel cell, the CO concentration must be decreased to about 0.5% by using a CO transformer, and a CO selective oxidation reaction must be caused by using a CO selective oxidizing unit to decrease the CO concentration to about 10 ppm. However, separately providing the CO transformer and CO selective oxidizing unit for the single-pipe cylinder type reformer is not preferable in terms of a reduction in size, an increase in efficiency, and starting characteristics.
The present invention has been made in consideration of the above problems in the prior art, and has as its first object to provide a single-pipe cylinder type reformer which prevents the generation of thermal stresses by liberating thermal displacement of outer and inner cylinders forming a reformer in the axial direction, prevents the occurrence of buckling of the inner cylinder and a deterioration in the performance of the reformer due to the buckling, in particular, and reduces a heat radiation loss from a combustion chamber through a cover plate.
It is the second object of the present invention to provide a single-pipe cylinder type reformer which produces a gas with a low CO concentration, operates efficiently, has good start-up characteristics, attains reductions in size and weight, and is thermally stable and efficient.
In order to achieve the first object of the present invention, according to the first aspect of the present invention, there is provided a single-pipe cylinder type reformer characterized by comprising an upright outer circular cylinder, a circular cylinder concentrically located inside the outer cylinder at a distance in a radial direction, a circular intermediate cylinder unit concentrically located between the outer cylinder and the inner cylinder at a distance in the radial direction, a circular radiation cylinder concentrically located inside the inner cylinder at a distance in the radial direction, a burner fixed to one end portion of the reformer in an axial direction to be located in the center of the radiation cylinder in the radial direction, and a plurality of annular flow paths formed in laminar shapes in the radial direction between the inner cylinder and the intermediate cylinder unit and between the intermediate cylinder unit and the outer cylinder, the annular flow paths being at least partly filled with a reforming catalyst serving as a reforming catalyst layer and communicating with each other, wherein end portions of the outer and inner cylinders in the axial direction which are located on a side opposite to a position where the burner is fixed are sealed with different cover plates such that the cover plates are located at a predetermined distance away from each other, thereby forming a double-bottom structure.
In the first aspect of the present invention, the burner is fixed to an upper end of the reformer, and the cover plates are respectively mounted on lower ends of the outer and inner cylinders.
The burner is fixed to a lower end of the reformer, and the cover plates are respectively mounted on upper ends of the outer and inner cylinders.
In the first aspect of the present invention, a steam generator is further disposed inside or outside the reformer.
The single-pipe cylinder type reformer according to the first aspect of the present invention is used for a fuel cell.
In order to achieve the first and second objects, in a single-pipe cylinder type reformer comprising an upright outer circular cylinder, a circular cylinder concentrically located inside the outer cylinder at a distance in a radial direction, a plurality of circular intermediate cylinders concentrically located between the outer cylinder and the inner cylinder at distances from each other in the radial direction, a circular radiation cylinder concentrically located inside the inner cylinder at a distance in the radial direction, a burner fixed to one end portion of the reformer in an axial direction to be located in the center of the radiation cylinder in the radial direction, and a plurality of annular flow paths formed in laminar shapes in the radial direction between the inner cylinder and the innermost intermediate cylinder, between the adjacent intermediate cylinders, and between the outermost intermediate cylinder and the outer cylinder, the annular flow paths being at least partly filled with a reforming catalyst serving as a reforming catalyst layer and communicating with each other, the present invention has the following characteristic aspects.
1. A steam generator is disposed inside a radiation cylinder, and the steam generator is heated through the wall surface of the radiation cylinder.
2. A preheat layer filled with a heat transfer promoting member is disposed before the upper portion of a reforming catalyst layer filled with a reforming catalyst.
3. The heat recovery layer is disposed around a reforming catalyst layer to be connected thereto at the lower end. A reformed gas is made to ascend through the heat recovery layer to transfer the heat of the reformed gas to the reforming catalyst layer.
4. The heat recovery layer is filled with ceramic balls each having a predetermined diameter.
5. The reformer includes a heat recovery layer which is disposed around a reforming catalyst layer for reforming the reformation material gas to be connected thereto at the lower end, and transfers the heat of a reformed gas to the reforming catalyst layer as the reformed gas ascends inside the heat recovery later, a CO converter catalyst layer (to be also referred to as a shift layer hereinafter) which is disposed around the heat recovery layer to be connected thereto at an upper portion, and reduces CO in the reformed gas as the reformed gas descends inside the CO converter catalyst layer, a second shift layer which is disposed around the shift layer to be connected thereto at a lower portion, connected to a CO selective oxidizing catalyst layer (to be also referred to as a PROX layer hereinafter) for reducing CO in the reformed gas by causing it to react with oxygen in air as the reformed gas ascends inside the CO selective oxidizing catalyst layer and/or the shift layer at a lower portion, and reduces CO in the reformed gas as the reformed gas ascends inside the second shift layer, and a cooling fluid path which is formed between the shift layer and the PROX layer and/or the second shift layer, forms a descending path from the inlet for the reformed gas on the PROX layer and/or second shift layer side, reverses the reformed gas at the lower end of the descending path, and serves as an ascending path on the shift layer side to allow a cooling fluid to pass.
6. An upper portion of a heat recovery layer, i.e., part of the downstream side, serves as a sub-CO converter catalyst layer (sub-shift layer).
7. Combustion air, a reformation material gas to be fed into the reforming catalyst layer, gaseous or liquefied reforming water, or a fluid as a combination thereof is fed into the cooling fluid path.
8. A predetermined gap is ensured between the outer wall surface of the heat recovery layer and the inner wall surface (inner cylinder) of the shift layer, and the bottom portion of the inner wall (inner cylinder) of the shift layer is separated from the bottom portion of the outer wall of the heat recovery layer, thereby forming a double-bottom structure.
9. An air path is formed in the outermost annular flow path formed between the circular outer cylinder and the outermost intermediate cylinder and the bottom portion of the annular flow path, an air inlet is formed in at least the side wall or bottom plate of the outermost intermediate cylinder, and air is evenly supplied into an annular path formed between the outermost intermediate cylinder located on the side and the second outermost intermediate cylinder adjacent to the outermost annular flow path.
10. The PROX layer is made up of a PROX layer and an air mixing layer which is formed before the PROX layer to mix the oxygen and reformed gas, and the air mixing layer is formed at the position of the air inlet.
11. Reforming water fed into the cooling fluid path cools the shift layer and PROX layer and/or second shift layer which are in contact with the cooling fluid path, and is heated and evaporated by reaction heat.
12. A heat insulator is charged in between the bottom portion or inner cylinder and the intermediate cylinder, between the respective intermediate cylinders, and the intermediate cylinder and the outer cylinder, as needed.
13. The shift layer and PROX layer and/or second shift layer are shorter than the heat recovery layer in the axial direction.
14. The shift layer and PROX layer and/or second shift layer are connected such that a reformed gas from the shift layer is temporarily discharged into an air path formed outside the PROX layer and/or second shift layer, merges with air in the air path, and is fed into the PROX layer and/or second shift layer again.
15. The reformer described above is used as a hydrogen source for a polymer electrolyte fuel cell.
16. Operation of the single-pipe cylinder type reformer described above includes
a. the step of supplying saturated or superheated steam extracted from a saturated or superheated steam outlet of the steam generator, together with a reformation material gas, in start-up operation in which an internal temperature of the reformer is not more than a predetermined temperature, the step of closing the saturated or superheated steam outlet and opening a wet steam outlet of the steam generator to supply wet steam together with a reformation material gas when the internal temperature exceeds the predetermined temperature, and the step of performing steam reforming for a reformation material gas in the annular flow path, and
b. regulating the opening degree of the regulating valve disposed at the wet steam outlet in accordance with a variation in operation state so as to maintain the inflection point temperature of the shift layer and the temperatures of the PROX layer and/or second shift layer at a predetermined temperature.
According to the present invention, the following excellent effects can be obtained.
(1) Since the thermal displacement of the outer and inner cylinders in the axial direction is liberated, deformation of each cylinder due to a thermal stress, especially buckling of the inner cylinder, and a deterioration in the performance of the reformer due to the buckling can be prevented.
(2) Since the combustion chamber is partitioned off from the outside of the reformer by multiple cover plates (bottom plates) including gas stagnation spaces, the heat insulating effect improves, and a heat radiation loss from the reformer is suppressed, thus improving the performance of the reformer.
(3) The formation of the preheat layer before the reforming catalyst layer can obviate the necessity of a material preheating unit and reduce the heat consumption.
(4) The inlet of the preheat layer is brought near the outlet of the heat recovery layer to lower the temperature at the outlet of the heat recovery layer. This makes it possible to directly connect the reforming catalyst layer to the CO converter catalyst layer.
(5) The formation of the steam generator which is heated by using part of the radiation cylinder as a heat transfer surface allows a boiler to be integrally incorporated in a compact reformer, thus preventing damage due to overheating and allowing efficient use of the heat quantity of a combustion exhaust gas. Therefore, the thermal efficiency can be improved.
(6) Since the heat recovery layer is filled with a heat transfer promoting filler, the heat recovery efficiency can be improved, and the temperature at the outlet can be lowered.
(7) Since the cooling fluid path is formed between the CO converter catalyst layer and the CO selective oxidizing catalyst layer and/or second shift layer, the CO selective oxidizing catalyst layer and/or second shift layer can also be integrally formed. In addition, reaction heat from the CO converter catalyst layer and CO selective oxidizing catalyst layer and/or second shift layer can be recovered, and hence the efficiency can be improved. Furthermore, undesirable side reactions can be suppressed. By changing the thermal load supplied to the cooling fluid path, the temperatures of the shift layer and CO selective oxidizing catalyst layer and/or second shift layer can be maintained within a predetermined range.
(8) The wall surface of the heat recovery layer and the wall surface of the CO converter catalyst layer are separately formed, and a gap is ensured between the wall surfaces. This improves the heat insulating properties between the two layers, improves the recovery efficiency in the heat recovery layer, and suppresses an increase in the temperature of the CO converter catalyst layer.
(9) Since air for the CO selective oxidizing catalyst layer and/or second shift layer is fed into the air path formed between the outer cylinder and the CO selective oxidizing catalyst layer and/or second shift layer, and air supply ports are formed in the CO selective oxidizing catalyst layer and/or second shift layer, air can be evenly supplied to the CO selective oxidizing catalyst layer and/or second shift layer, and a hydrogen loss can be reduced. In addition, a heat radiation loss can be reduced by heat insulation. The air mixing layer for mixing air in the CO selective oxidizing catalyst layer and/or second shift layer is formed by charging a filler. This makes it possible to mix a reformed gas with air without using any mixing unit and reduce the hydrogen loss.
(10) Since reforming water is evaporated in the cooling fluid path between the CO converter catalyst layer and the CO selective oxidizing catalyst layer and/or second shift layer, a boiler can be formed without using any fuel. A sufficient cooling ability with respect to the CO converter catalyst layer and CO selective oxidizing catalyst layer and/or second shift layer can be obtained. The arrangement of a nozzle or the like can be simplified.
(11) By regulating the regulating valve of the steam generator, the amount of wet steam is changed to quicken the temperature rise time in start-up operation. In steady operation, reaction heat and sensible heat of a reformed gas are recovered to improve the efficiency. Furthermore, the temperatures of the CO converter catalyst layer and CO selective oxidizing catalyst layer and/or second shift layer can be regulated.
(12) Since the concentration of carbon monoxide in a reformed gas can be reduced to a predetermined value or less, the reformer can be used as a hydrogen generator for a polymer electrolyte fuel cell. This makes it possible to obtain a compact, high-efficiency fuel cell.
(13) Since the flow path comprising the CO converter catalyst layer and CO selective oxidizing catalyst layer and/or second shift layer is shorter than the heat recovery layer, an excessive rise in the temperature of the CO converter catalyst layer can be prevented, and the temperature can be maintained at a proper temperature. Therefore, no reaction is inhibited.
(14) Since the reformer is filled with an insulating material at proper portions, heat radiation from the reformer can be prevented, and the thermal efficiency can be improved. In addition, each portion is properly insulated from heat, and hence the temperature of each portion can be maintained at a proper temperature.
(15) The formation of the CO converter catalyst layer on the downstream side of the heat recovery layer can quickly raise the temperature of the CO converter catalyst layer. Therefore, a reaction can be quickly caused in the CO converter catalyst layer at start-up. This makes it possible to quickly start the reformer.
(16) Since a reformed gas passing through the CO converter catalyst layer and air can be sufficiently agitated, reactions can be reliably and efficiently caused in the CO selective oxidizing catalyst layer and/or second shift layer, thus improving the hydrogen production efficiency of the reformer.
The above and other many objects, aspects, and merits of the present invention will be apparent to those skilled in the art from the following detailed description exemplifying the preferred embodiments conforming to the principle of the present invention and the accompanying drawings.